JavaScript permutation

permute.js

// a + permute(b, c, d);
// a + b + permute(c, d);
// a + c + permute(b, d);
// a + d + permute(b, c)

function permute(str) {
    var used = new Array(4);
    var list = str.split('');
    var out = [];
    doPermute(used, list, 0, out);
}

function doPermute(used, list, start, out) {
    if (start == list.length) {
        return console.log(out.join(''));
    }

    for (var i=0; i < list.length; i++) {
        if (used[i] === true) {
            continue;
        }

        used[i] = true;
        out.push(list[i]);
        doPermute(used, list, start + 1, out);
        used[i] = false;

        out.pop();
    }
}

//permute(list);
permute('abcd');